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Thread: SPDT or DPDT

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    SPDT or DPDT

    Ok a real newbie question. Attempting my first panels. I read in some post (somewhere) that there was in fact little difference in SPDT switches and DPDT switches. This contributor suggested that the second pole in a DPDT switch was rarely used. Is this correct. If not what is the second pole used for? I am assuming these switches give one set of parameters when "up" and a different set when "down".

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    150+ Forum Groupie andarlite's Avatar
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    A DPDT switch is just 2 SPDT on a single switch. This is just an example, but let's say you have a SPDT switch to turn on your right fuel pump and another SPDT switch to turn on your left fuel pump. If you are always turning both on/off at the same time time (and you're tired of always having to flip 2 switches), you could get rid of the SPDT switches and wire both fuel pumps to a DPDT switch. Now by flipping one switch, you turn on/off both fuel pumps.

    Regards,
    Henry

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    Thank you for your explanation. I think I will stick to SPST and SPDT for now!! At least until I get a little more experience. Currently I am building a "PedoHead" which is a mixture of pedestal and overhead (overhead just not viable at the moment). This will simulate all the controls I need/want at the moment. I do not wish to start from cold and dark just now. Instead I start at gate with engines running but on my "pedohead" I will have radios, lights, Radar Contact panel, FDC panel, MZALFOTRI (for PMDG 737), 3 Go Flight Units etc. Lots of work ahead.
    Bill

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    Smile im sure you know this already but gets it clear in my own mind!

    SPST - single pole,single throw (one position switch eg on-off)
    SPDT - single pole,double throw (2 position switch eg on,off,auto)

    DPST- double pole,single throw (basically 2x SPST connected to same switch lever)
    DPDT- double pole, double throw(2x SPDT on same switch lever)

    I guess you could have a triple TPST or TPDT.....
    Steve
    another bedroom boeing.....

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    The other reeason some people use a DPDT switch is when they use seperately powered annunciators. The DPDT allows two circuits to be used without interfering with each other.

    Rob

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    2000+ Poster - Never Leaves the Sim Michael Carter's Avatar
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    I use those. One side for the annunciator, the other side for signal.

    And there are switches with as many as eight poles. The fire handles on the 727 and 737-200 have very long push-pull type multiple pole swithes.
    Boeing Skunk Works
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    1000+ Poster - Fantastic Contributor Tomlin's Avatar
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    I plan to use these for the Avionics and Battery switches for my Learjet sim. One side of the switch will be connected to the REAL power and the other side will be connected to the SIMULATED power/Avionics (FS) and this will prevent the screens from showing the LCD backlighting when the avionics arent turned on in the sim. Also, this allows for a person to build in some electrical logic without having to use PM Systems, such as how the BATT switch has to be on in order for the Avionics Master to be effective.
    Eric Tomlin-
    Learjet 45 Builder
    www.flightlevel180.org

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    300+ Forum Addict luisgordo's Avatar
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    Just found this link searching something else, and thought it might be useful:
    http://en.wikipedia.org/wiki/Switch
    Luis Gordo
    Instructor StationTM - www.iStationGordo.com

  9. Thanks W9XE/Project777, Matt Olieman thanked for this post

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